The present invention is a process for the thermal disproportionation of arylhalosilanes containing at least one hydrogen bonded to silicon. The process involves heating the arylhalosilanes in liquid phase to a temperature within a range of about 250.degree. C. to 450.degree. C. The present process is particularily useful for the disproportionation of phenyldihalosilanes to diphenyldihalosilanes.
It is known that disproportionation of monoaryldichlorosilanes occurs in the presence of Friedel-Crafts type catalysts. For example. Wagner. U.S. Pat. No. 2,746,981, issued May 22. 1956, describes a process for the disproportionation of an aryldichlorosilane containing one aryl group and one hydrogen group. by heating the aryldichlorosilane to a temperature of at least 50.degree. C. and a pressure not to exceed atmospheric in the presence of a Friedel-Crafts type catalyst taken from the class consisting of aluminum chloride and boron chloride, and recovering a diarydichlorosilane.
Japanese Patent 62263189, Published Nov. 16, 1987, describes the use of Lewis acid compounds for the disproportionation of aryldihalosilanes under reduced pressure. The catalysts used are described as Lewis acid compounds such as metal halides and aryl metal compounds. Examples of catalysts described in the Japanese patent are aluminum chloride, aluminum bromide, triphenylborane, and tolylborane.
In general, these processes involving the use of catalyst require that the catalyst either be removed or neutralized prior to distillation to separate desired product. If the catalyst is not removed, the desired product can be disproportionated during the distillation process. reducing process yield. In addition, catalysts such as AlCl.sub.3 easily sublime coating the processing equipment. Therefore, it is an objective of the present invention to provide a disproportionation process that does not present these problems typically associated with the use of catalysts.
Gilman et al., J. Org. Chem. 23:326-328 (1958), describes the uncatalyzed disproportionation of Ph.sub.2 SiH.sub.2 at 100.degree. C. to 300.degree. C. at atmospheric pressure.
Eaborn et al., J. Organometal. Chem. 4:489 (1965), describes a process where phenyltrimethylsilane and trichlorosilane are reacted at 500.degree. C. in the gas phase to give phenyltrichlorosilane and trimethylsilane.
The present process comprises the thermal disproportionation of arylhalosilanes containing at least one hydrogen atom bonded to silicon by heating to a temperature of 250.degree. C. to 450.degree. C. in the absence of a catalyst. The process avoids the aforementioned problems typically associated with the use of catalysts to disproportionate arylhalosilanes.